1. Field of the Invention
The present invention relates to a clamp assembly for attachment to a lifting apparatus of a lift truck, and more particularly, to a pivot frame roll clamp assembly for picking up, transporting and stacking large rolls of paper.
2. Description of the Related Technology
A variety of pivoted paper roll clamp assemblies have been utilized in the past wherein the arms of the clamp shift between an equal arm length position where the opposing clamp arms extend an equal distance forward of the lift truck, and an unequal arm length position where one clamp arm extends a greater distance forward of the lift truck than the other clamp arm. The unequal arm extension position is needed when a paper roll is lying on a horizontal surface, such as the floor, so that the longer upper clamp arm can overreach the lower clamp arm in order to assume substantially diametrically opposed positions for grasping the roll firmly to pick it up. The equal arm extension position is needed to facilitate placement of a vertical roll in close proximity with other vertically positioned rolls in a compact array, as well as to remove such a roll from the array.
One such prior art roll clamp includes the paper roll load clamp having a power-actuated pivotal subframe shown in House, U.S. Pat. No. 4,435,119. The House roll clamp includes a subframe that is pivotally connected to the rotatable frame of the clamp near the axis of rotation. Clamp arms are pivotally mounted upon the subframe on each side of the pivotal connection between the subframe and the rotatable frame. A hydraulic subframe actuator pivots the subframe angularly in relation to the rotatable frame, thereby angularly shifting the clamp arms as a single unit relative to the rotating frame. One of the clamp arms is longer than the other to provide for the desired unequal arm extension necessary to engage a roll positioned on a horizontal surface. Because of the unequal arm lengths, the arms must travel through varying arcuate motion to achieve proper closure.
Several disadvantages are present in the prior art clamps. Because the subframe of clamp shown in U.S. Pat. No. 4,435,119 is pivotally connected to the rotatable frame at a single midpoint, shifting between positions of equal arm extension and unequal arm extension is often jerky and violent. In many prior art paper roll clamps, the center of gravity of the roll may be shifted forward during movement between the unequal arm extension position and the equal arm extension position causing instability of the lift truck.
For the foregoing reasons, there is a need for a lift truck roll clamp assembly where the forward movement of the roll's center of gravity is minimized as the clamp shifts from a position of unequal arm extension to a position of equal arm extension. There is also a need for a roll clamp wherein the clamp can be smoothly shifted between the unequal arm extension position and the equal arm extension position.